Production of cellulose esters



Patented Nov. 28, 1933 UNITED STATES 1,936,589 PRODUCTION or CELLULOSE ESTERS Henry Dreyfus, London, England No Drawing. Application July as, 1930, Serial No. 470,230, and in GreatBritain August 2,

20 Claims.

This invention is a continuation in part of U. S. application S. No. 328,306 dated 24 December 1928, now Patent No. 1,911,069, May 23, 1933 and relates to new or improved processes for the production of cellulose acetates or other cellulose esters, e. g. cellulose propionate and cellulose butyrate.

In the said U. S. application S. No. 328,306 dated 24 December 1928 processes are described for the pretreatment of cellulosic materials prior to their esterification, which pretreatment consists in treating the cellulosic materials with hydrochloric acid, hydrobromic acid or hydriodic acid, or mixtures thereof, in quantity (calculated as hydrohalide) not substantially exceeding of the weight of the cellulose, while avoiding disintegration.

The said U. S. application further describes processes in which hydrohalide acid isused in conjunction with halides, and particularly chlorides of iron (ferric), tin (stannic), cobalt, nickel, manganese or copper and in which the pretreatment is applied in conjunction with, i. e. simultaneously with or separately from, pre treatments with organic acids and particularly lower aliphatic acids, e. g. formic or acetic acid. I have now found, and this constitutes the improvement of the present invention, that very good results may be obtained even though the hydrohalide acid be used a proportion of less than 2% of the weight of the cellulose. e. g. in a proportion of between 1 and 2%. The pretreatment may be carried out in conjunction, either simultaneously or separately, with a pre treatment with organic acids, e. g. acetic acid, and/or with a pretreatment with ferric, stannic, cobalt, nickel, manganese or copper halides. The methods of. pretreatment according to the present invention offer the greatest advantages when the subsequent esterificaticn 'is to be effected in the presence as catalysts of the various halide salts referred to above, alone or in conjunction with hydrohalide acids. These processes of esterificationusing halide catalysts are des cribed'in my prior U. S. applications SNos. 301,927 dated 24 August 192 321,750 dated 24.- November 1928 and 321,751 dated 24 November As initial materials for treatment according to the present invention, cotton or other cellu loses or other cellulosic materials may be em ployed. Such materials may contain the usual amounts of moisture, for instance 4% to 6 or 8%,01 may befreed from moisture by drying. Wood pulps, or bamboo, esparto or other mate rials containing encrusting matter and from, which the lignin, pentosan, resin and like constituents have been substantially removed, as-for example in sulphite pulp, soda pulp OrLsulphate pulp may be employed, but such materials are preferably subjected to arr-alkaline purifying treatment prior to the pretreatment contemplated in the present invention. The alkaline purifying treatment may for example 'be efiected in the manner described in my U. S. Patent No. 1,711,110, for instance with caustic alkali of low concentration, such as 3% or under, with heating or boiling, or with caustic alkali of higher concentration such as 15-20%, in the cold or with only slight heating. A material so treated 9 may then besubjected to the processes of pretreatment of the present invention in substitution for the lower fatty acid treatment of the said U. SIPatent No. 1,711,110.

.The pretreatment with the hydrohalide acid with or without organic acid and/or halide salts is effected at any suitable temperatures which do not result in disintegration of the cellulose, and particularly at ordinary temperatures or withcooling. 1 9 The acetylation or other 'esterification'may be effected in' any suitable manner, and particu larly by processes employing metallic halides with or without hydrohalide acid, see my prior U. S. applications S. Nos. 301,927, 321,750 and 321,751. I have further found that very valuable results .may be obtained by utilizing during at least part of the esterification catalysts containingiron'in a proportion in excess of that equivalenttothe chloride or other acid radicle. This method forms the subject matterof my co-pending application S. No. 470,229 filed July 23, 1930. "By such means the range of esterificationtemperatures which may be employed without resulting in serious or substantial degradation to'the-cellu- 9 lose molecule is considerably extended and temperatures up to 75 or even up to 90 C'. or higher may be employed. The actual ratio ofchloride or other acid radicle to iron may vary from an, insignificant'proportion to almost anequivalent proportion. Proportions intermediate between these two valuesy'e. g. a proportion of'chloride or other acid radicle equivalent to half the iron present, give very satisfactory results. The excess of iron may be introduced into the acetylating or esteriiying mixture, or into aconstituent thereof before making up the mixture, in any suitable manner. Forexample ferric oxide or ferric hydroxide, preferably freshly prepared, may be introduced as such into theacetylating or esterifying mixture, or into a constituent thereof, preferably already containing ferric chloride or ferric bromide; or alternatively the iron may be introduced into such a mixture or constituent thereof wholly in the form of chloride or bromide, or partly in the form of chloride or bromide and partly in the form of another salt, and a part or whole of the chloride or other, acid radicle neutralized by suitable addition of alkali or any alkaline reagent. Such alkali or alkaline reagent is preferably so chosen that no precipitation of iron takes place in the esterifying mixture or constituent thereof. As a further alternative, the catalyst, already containing an excess of iron over the acid radicle, may be introduced as a whole, e. g. in the form of a basic salt, into the esterifying mixture or a'constituent thereof.

As a further modification of the invention, the above catalysts, i. e. catalysts containing an excess of iron over the acid radicle, may be present during only a part of the esterification, e. g. during the latter part. In such a case the esterification may for instance be begun with ferric chloride alone or ferric chloride mixed with hydrochloric acid as catalyst, and the chloride iron wholly or partly neutralized in one or more stages during the esterification. Such two or multi-stage processes may, for example, be started with any desired quantities of ferric chloride or of ferric chloride and hydrochloric acid relative to the cellulose. For example ferric chloride may be used alone in quantities varying from 1 to 2% up to 10, 20 or even 30%, while ferric chloride and hydrochloric acid are preferably used in quantities of under 15% of each on the cellulose and may even be used in quantities of less than 2% on the weight of the cellulose. In carrying out the esterification in stages with such catalysts of varying acidity, the temperature may be raised in the various stages; e. g. in the first stage in which the acidity is relatively high, comparatively low temperatures such as 15-20 or 30 C. may be employed, while in subsequent stages employing catalysts of decreasing acidity higher temperatures e. g. 50 or C. or or even 90 C. may be employed. Furthermore, such varying temperatures may be employed, even though no neutralization of the catalyst takes place during the actual esterification.

The actual acetylation or esterification may be carried out so that the ester is produced in solution or may be carried out in suspension in presenceof liquid diluents or may be effected with 7 the aid of vaporous esterifying agents.

The'cellulose acetates or other cellulose esters produced may be subjected to processes of further treatment or ripening, such processes being preferably effected in presence of the catalysts used in the actual esterification. The ripening treatment may, for example, be effected at ordinary temperatures or at somewhat increasedtemperatures or even relatively high or high temperatures, such as or 100 C. or more. In the case of using high or relatively high temperatures,

free mineral acidity is preferably avoided or reduced to very small proportions. If the esterification has been effected or completed in the presence of catalysts having comparatively small free mineral acidity, neutralization will not be necessary, but in other cases as indicated, ripening at high temperatures is preferably effected after neutralization.

The cellulose acetates or other cellulose esters produced by the present processes may be utilized either as primary or secondary esters, and in their primary esterification or ripening solutions or suspensions or after separation therefrom, for the production of artificial silks or fibres, films, plastic masses, moulding powders, molded articles, etc.

The following examples show the best methods known to me for carrying the invention into effect, but they are not to be considered as limiting the invention in any way:

Example 1 100 parts of cotton linters are sprayed with a mixture of 20 parts of glacial acetic acid and 3 parts of 33% aqueous hydrochloric acid and allowed to standwith occasional stirring for about 2 hours at or inary temperature. The pretreated material is then introduced into an acetylator in a mixture containing 800 parts of glacial acetic acid, 450 parts of acetic anhydride and 20 parts of ferric chloride. The acetylation is begun in the cold and the temperature allowed to rise at the end of about 2 hours to 30 to 40 C., at which stage 15 parts of freshly precipitated ferric hydroxide are added. The acetylation is then completed at a temperature of 40 to 60 C. until solution is complete. 7

Example 2 10d parts of cotton linters pretreated with hydrochloric acid and glacial acetic acid as described in Example 1 are introducedinto a mixture of 600 parts of glacial acetic acid 450 parts of acetic anhydride and 25 parts of crystallized ferric chloride. The reaction is conducted at a temperature which may vary from ordinary atmospheric temperature to 35 or 40 C. with constant mixing or stirring until solution is complete. The cellulose acetate may then be further treated or worked up in any desired manner.

The term disintegration as used in the description and hereinafter in the claims is to be construed to mean loss of structure. 1

What I claim and desire to secure by Letters Patent is: p

1. Process for the production of carboxylic acid esters of cellulose, comprising treating materials consisting substantially of cellulose, while avoiddisintegration, with less than 2% of their weight of hydrogen halide and thereafter esterifymg.

2. Process according to claim 1, wherein the cellulosic materials are also pretreated with lower aliphatic acids.

3. Process according to claim 1, wherein the l cellulosic materials are also pretreated with metallic halides.

4. Process for the production of carboxylic acid esters of cellulose, comprising first treating chemical wood pulps with caustic alkali and thereafter treating them, while avoiding disintegration, with less than 2% of their weight of hydrogen halide.

5. Process for the production of cellulose acetate, comprising treating materials consisting substantially of cellulose, while avoiding disintegration, with less than 2% of their weight of hydrogen chloride and thereafter esterifying With acetic anhydride.

5. Process for the production of cellulose acetate, comprising treating materials consisting substantially of cellulose, while avoiding disintegration, with less than 2% of their weight of hydro gen chloride and with a lower fatty acid and thereafter esterifying with acetic anhydride.

'7. Process according to claim 6, wherein the acetylation is effected in presence of a metallic chloride catalyst.

8. Process according to claim 6, wherein the acetylation is efiected in presence of a metallic chloride and hydrochloric acid.

9. Process according to claim 6, wherein the acetylation is effected in presence of ferric chloride.

10. Process according to claim 6, wherein the acetylation is efiected in presence of ferric chloride and hydrochloric acid.

11. Process for the production of carboxylic acid esters of cellulose, comprising treating materials consisting substantially of cellulose at temperatures which avoid disintegration with less than 2% of their weight of hydrogen halide and thereafter esterifying.

12. Process according to claim 11, wherein the cellulosic materials are also pretreated with lower aliphatic acids.

13. Process according to claim 11, wherein the cellulosic materials are also pretreated with metallic halides.

14. Process for the production of carboxylic acid esters of cellulose, comprising first treating chemical wood pulps with caustic alkali and thereafter treating them at temperatures which avoid disintegration with less than 2% of their weight of hydrogen halide.

15. Process for the production of cellulose acetate, comprising treating materials consisting substantially of cellulose at temperatures which avoid disintegration with less than 2% of their weight of hydrogen chloride and thereafter esterifying with acetic anhydride.

16. Process for the production of cellulose acetate, comprising treating materials consisting substantially of cellulose at temperatures which avoid disintegration with less than 2% of their weight of hydrogen chloride and with a lower fatty acid and thereafter esterifying with acetic anhydride.

17. Process according to claim 16, wherein the acetylation is efiected in presence of a metallic chloride catalyst.

18. Process according to claim 16, wherein the acetylation is effected in presence of a metallic chloride and hydrochloric acid.

19. Process according to claim 16, wherein acetylation is effected in presence of ferric chloride.

20. Process according to claim 16, wherein the acetylation is effected in presence of ferric chloride and hydrochloric acid.

HENRY DREYFUS.

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